Idk, I didn’t read this book. But I lived a similar version of that reality in a conservative southern US town. My home life was challenging. I sold drugs and generally was a rebellious troublesome teenager. All the officials in my school and local law enforcement gave me kind slaps on the wrist compared to what they could/should have. I had to assume they were trying to get me to a point of adulthood without having life ruining consequences weighing me down. I straightened up by around 17-18 but there were certainly a few times between 14-17 I could have been charged for adult felony crimes and was let off the hook, never even spent a night in a juvenile detention facility but I was made to flush a lot of drugs down some toilets a time or two. I think it used to be more common to let kids figure things out for themselves. I don’t think the similar levels of leniency would occur, it’s all zero tolerance.

A foreign student who is afraid of returning to her home country sounds like an ideal low-level drug dealer. They are legally vulnerable because they are afraid of being expelled from the country, and they have access to lots of potential buyers in their fellow students. And someone who is new and is looking for friends is more easily approached and recruited.

I've personally encountered some stories that were pretty much exactly that.

Vulnerable young people becoming low level drug dealers (often for lack of other options) isn't exactly a rare story.

I'm from Vienna (admittedly younger) but it seems believable. The place she picks up the drugs in the comic is "Café Camera" which is clearly a reference to "Camera Club" which was well-known for this in the 80s and 90s.

For some reason immigrant drug dealers in Europe doesn't really strain credulity very much.